When we ran a full service chassis fab/turn-key hot rod shop a number of years ago, it was always useful to have threaded things around to weld into the frame for some kind of mount, etc.
Here’s a list of all our threaded things for your reference:
Rear Coilover Mount Plate
Product Details
Brand: Welder Series
MPN: 20294
Thickness: 3/16"
Hole size: 1"
2-1/2" x 1-5/8" with a 1" diameter hole, used in our rear coil over bracket kits.